Additive manufacturing method and support member design method

Abstract

To provide an additive manufacturing method and a design method for a support member that can simplify a support member removal step.SOLUTION: An additive manufacturing method for a metal laminate build article 2 having an opening 22 on a surface thereof has a build step of building a support member 3 and a metal laminate shaped article 2 on the member and a removal step of removing the support member 3 by a machine work. The building step is a step that repeats deposition of metallic powder and sintering and melting of the metallic powder by laser beam irradiation to build the support member 3 and the metal laminate build article 2. The opening 22 at an interface 10 of the metal laminate build article 2 and a part in contact with a vicinity of an outer edge 23 of the opening 22 of the support member 3 are not built to be a void part 31 the part of which is recessed from the interface 10.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an additive manufacturing method for a metal additive manufactured product having an opening on its surface, and a method for designing a support member for supporting a metal additive manufactured product used in the additive manufacturing method. [Background technology]

[0002] In recent years, metal additive manufacturing has been proposed as a means for easily manufacturing metal parts and the like. With metal additive manufacturing, metal parts having complex shapes can be easily obtained with fewer steps compared to conventional processing methods. There are two main methods known for metal additive manufacturing. One is the metal deposition method, in which metal powder is deposited only in a predetermined place and sintered or melted by irradiating it with laser light. The other is the powder bed method, in which metal powder is deposited on one side of the base plate of a metal additive manufacturing device and sintered or melted by irradiating it with laser light only in a predetermined place. In both methods, metal additive manufacturing products are manufactured by repeatedly depositing metal powder and sintering or melting the metal powder by irradiating it with laser light, and stacking layers of metal.

[0003] When metal parts having overhanging portions, such as T-, Y-, or H-shapes, are manufactured by metal additive manufacturing, support members are formed to support the metal additive manufacturing product in order to prevent defective manufacturing or distortion of the parts. In addition, support members may be formed between the metal additive manufacturing product and the base plate of the additive manufacturing device, regardless of whether the part has an overhanging shape or not.

[0004] When a metal additive manufacturing product is directly molded on a base plate, the surface of the metal additive manufacturing product that was in contact with the base plate may become uneven. In addition, when peeling the metal additive manufacturing product from the base plate after molding, the surface where the base plate and the metal additive manufacturing product are in contact may not be peeled cleanly, and part of the metal additive manufacturing product may remain on the base plate, causing unevenness on the surface of the metal additive manufacturing product. In these cases, when machining is performed to smooth the surface of the metal additive manufacturing product, the product will be smaller than the target dimensions.

[0005] In such a case, a support member is provided as a sacrificial member between the base plate and the metal additive manufacturing product, and then the support member is removed to obtain a metal additive manufacturing product having a smooth surface and the target dimensions. The support member must be removed after being molded together with the metal additive manufacturing product, and removal can be performed using methods such as mechanical processing such as cutting and polishing, and chemical processing. From the viewpoint of reducing the burden of the manufacturing process, it is preferable that these removal steps are simpler or involve fewer steps, and studies are being conducted to simplify and facilitate the support member removal process.

[0006] For example, Patent Document 1 discloses a support member formed between a metal additive manufacturing product and a base plate of an additive manufacturing device. This document describes that the support member can be easily removed from the metal additive manufacturing product and the base plate by forming the support member into a honeycomb structure so as to be partially joined to the metal additive manufacturing product, or by providing the support member at a predetermined position. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2019-81923 A Summary of the Invention [Problem to be solved by the invention]

[0008] When the support member and the metal additive manufacturing product are partially joined, such as in the honeycomb structure described in Patent Document 1, the tools used for cutting, polishing, etc. of the support member are subjected to different loads intermittently between the parts in contact with the support member and the parts not in contact with the support member, and as a result, their lifespan is likely to be shorter than when they are subjected to the same load continuously.

[0009] Furthermore, when a metal additive manufacturing product has a through hole or a recessed portion recessed inward, and the opening of the through hole or recessed portion is located on the boundary surface with the support member, burrs may occur on the inside of the opening when the support member is removed by cutting, polishing, or the like. The presence of burrs in a metal additive manufacturing product may have adverse effects depending on the intended use of the product. The occurrence of burrs requires additional work to remove them, which is undesirable from the viewpoint of simplifying the support member removal process.

[0010] The present invention has been made in consideration of the above circumstances, and aims to provide a method for additive manufacturing of metal additive manufacturing products and a method for designing support members that can simplify the support member removal process. [Means for solving the problem]

[0011] The additive manufacturing method of the present invention is an additive manufacturing method for a metal additive manufactured product having an opening on its surface, the additive manufacturing method comprising a manufacturing step of manufacturing a support member and a metal additive manufactured product on the support member, and a removal step of removing the support member by machining, the manufacturing step being a step of manufacturing the support member and the metal additive manufactured product by repeatedly depositing metal powder and sintering or melting the metal powder by irradiating it with laser light, and the support member has an opening at the interface with the metal additive manufactured product and a portion adjacent to the outer edge of the opening that is not manufactured, and these portions are formed as voids recessed from the interface.

[0012] In the present invention, it is preferable that the cross section of the gap portion parallel to the stacking direction be formed into a rectangular shape in the molding step.

[0013] Furthermore, in the present invention, the vicinity of the outer edge is preferably within a range of up to 1.0 mm from the outer edge of the opening.

[0014] In the present invention, a surface that is inclined with respect to the boundary surface with the support member may be formed on the outer edge of the opening of the metal additive manufacturing product in the modeling step.

[0015] The support member design method of the present invention is a method for designing a support member for supporting a metal additive manufacturing product, used in an additive manufacturing method for a metal additive manufacturing product having an opening on its surface. The additive manufacturing method is a method in which deposition of metal powder and sintering or melting the metal powder by irradiating with laser light are repeated to form a support member and a metal additive manufacturing product on the support member, and then the support member is removed by machining. The shape of the support member is set so that the opening at the interface with the metal additive manufacturing product and the portion in contact with the outer edge of the opening form a void recessed from the interface. Effect of the Invention

[0016] By configuring the additive manufacturing method and support member design method of the present invention in this way, it is possible to suppress the occurrence of burrs at the openings when manufacturing a metal additive manufacturing product having an opening on its surface, and to simplify the support member removal process. [Brief description of the drawings]

[0017] [Figure 1] FIG. 2 is a cross-sectional view of a shaped article with supports. [Diagram 2] FIG. 1 is a cross-sectional view of a metal additive manufacturing product with the support member removed. [Diagram 3] 1A-1C are cross-sectional views of various supported shaped articles. [Figure 4] 1 is a process diagram of an additive manufacturing method according to the present invention. [Diagram 5] 3(a) and its enlarged view. FIG. [Figure 6] FIG. 1 is a schematic diagram showing an example of a molding process using a powder bed method. [Figure 7]This is a design drawing of a supported object. [Figure 8] 1 is an image of the entire machined surface after removal of the support member. [Figure 9] 13 is a magnified image of the opening after the support member has been removed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] An example of a metal additive manufacturing product and a supporting member (hereinafter also referred to as a "supported product") manufactured by the additive manufacturing method according to the present invention will be described with reference to Fig. 1. Fig. 1(a) is a perspective cross-sectional view of a cross section parallel to the layering direction of a supported product 1. Fig. 1(b) is an enlarged cross-sectional view of the periphery of an opening in Fig. 1(a). As shown in FIG. 1(a), the supported shaped product 1 is composed of a metal additive manufacturing product 2 and a support member 3. The metal additive manufacturing product 2 has two hollow cylindrical through holes 21 inside. One end of the through holes 21 is open, and the other end is covered by the support member 3. This other end opens when the support member 3 is removed, becoming an opening 22. The opening 22 is in contact with a surface (boundary surface 10) that becomes the surface of the metal additive manufacturing product when the support member 3 is removed. The cross section of the through holes 21 perpendicular to the layering direction is circular. Furthermore, the through holes 21 are provided perpendicular to the boundary surface 10.

[0019] 1(b), the portion of the support member 3 that contacts the opening 22 and the vicinity of the outer edge 23 of the opening 22 at the boundary surface 10 is not shaped. This portion is recessed toward the support member 3 side from the boundary surface 10, forming a void portion 31. The void portion 31 is hollow and dome-shaped, and its cross section parallel to the stacking direction is, for example, approximately semicircular.

[0020] The outer edge 23 of the opening 22 is the inner periphery of the opening 22 at the boundary surface 10. In addition, in the present invention, "the vicinity of the outer edge of the opening" means a region that is outside the outer edge 23 of the opening 22 and close to the outer edge 23 when the boundary surface 10 is viewed in a plan view. The range of this region is at least a range that can be molded as an overhang shape in which the support member 3 is not molded directly below it. The outer edge 32 of the gap 31 of the support member 3 at the boundary surface 10 coincides with the outer edge of this region. A specific range of this region is, for example, a range from the outer edge 23 to 1.0 mm, and preferably a range from the outer edge 23 to 0.25 mm to 0.50 mm. Note that, when the shape of the outer edge 23 of the opening 22 is circular, the outer edge 32 of the gap 31 can be arranged, for example, concentrically outside the outer edge 23 of the opening 22.

[0021] A metal additive manufacturing product in which the support members have been removed from the supported shaped product shown in Fig. 1 will be described with reference to Fig. 2. Fig. 2(a) is a perspective view of a cross section parallel to the lamination direction of the metal additive manufacturing product 2 after the support members have been removed. Fig. 2(b) is an enlarged cross-sectional view of the periphery of the opening in Fig. 2(a). After the support members are removed, the metal additive manufacturing product 2 has the support members completely removed, and what was the boundary surface with the support members becomes a new surface 11 of the metal additive manufacturing product 2. Surface 11 becomes a smooth surface due to machining. The inner diameter and shape of opening 22 do not change before and after the support members are removed. Furthermore, there are no protrusions such as burrs inside the through hole (rounded rectangular area in the figure).

[0022] The structure of the opening and the through hole in the metal additive manufacturing product 2 is not limited to the example shown in FIG. 1 and FIG. 2. For example, the opening and the through hole may be one or three or more. The shape of the outer edge of the opening may be a circle or an ellipse, or a polygon such as a square, a rectangle, a diamond, or a trapezoid. The opening may be an opening of a recess that does not penetrate the metal additive manufacturing product and is recessed inward. The through hole or the recess may be disposed at an angle to the boundary surface. The cross section perpendicular to the lamination direction of the through hole or the recess may have a different shape from the outer edge of the opening, and the inner diameter of the through hole or the recess may be freely selected. In addition, the through hole may be a hole in which a plurality of openings at the boundary surface are connected inside the metal additive manufacturing product.

[0023] In addition, the structure of the void in the support member 3 is not limited to the example shown in FIG. 1 and FIG. 2. For example, the cross section of the void parallel to the stacking direction can be freely selected from a semicircular shape, a rectangular shape, a trapezoidal shape, and the like. In the case of a trapezoidal shape, the void may be either a shape that expands or contracts from the opening toward the base plate described later. The shape of the outer edge of the void may be a circle, an ellipse, or a polygon such as a square, a rectangle, a diamond, or a trapezoid. The outer edge of the void may be provided at a fixed distance from the outer edge of the opening, or may not be provided at a fixed distance. The centers of the two shapes formed by the outer edges of the opening and the void may be the same or may not be the same.

[0024] An example of a support member manufactured by the additive manufacturing method according to the present invention is shown in Fig. 3. In Fig. 3, (a), (c), and (e) are cross sections parallel to the stacking direction, (b) is a cross section taken along line A-A' in (a), (d) is a cross section taken along line B-B' in (c), and (f) is a cross section taken along line C-C' in (e). Note that the opening of the metal additive manufacturing product in Fig. 3 is the end of a hollow cylindrical through hole. The supported shaped product in FIG. 3(a) comprises a metal additive manufacturing product 2a and a support member 3a having a void 31a whose cross section parallel to the lamination direction is rectangular. As shown in FIG. 3(b), in this embodiment, the outer edge 23a of the opening and the outer edge 32a of the void 31a are both circular and arranged concentrically. Making the cross section of the void 31a rectangular facilitates shaping. At the same time, the height of the void can be minimized, and the area where different loads are intermittently applied to the tool when removing the support member can be reduced.

[0025] The supported shaped product of Fig. 3(c) comprises a metal additive manufacturing product 2b and a support member 3b having a void 31b whose cross section parallel to the lamination direction is rectangular and whose outer edge is elliptical. As shown in Fig. 3(d), in this embodiment, the outer edge 23b of the opening is circular, and the outer edge 32b of the void 31b is elliptical. When removing the support member, by aligning the direction in which the machining force is received (the direction in which the cutting blade moves) with the long axis direction of the ellipse of the void, the overhang in the short axis direction can be reduced while ensuring the long axis distance to the opening, and the occurrence of burrs at the opening can be suppressed.

[0026] The supported shaped product of FIG. 3(e) includes a metal additive manufacturing product 2c having an opening whose inner surface is in contact with the boundary surface at a curved surface of a predetermined curvature, and a support member 3c having a void 31c whose cross section parallel to the lamination direction is rectangular. As shown in FIG. 3(f), in this embodiment, the outer edge 23c of the opening and the outer edge 32c of the void 31c are both circular and arranged concentrically. In addition, in this embodiment, the outer edge 23c of the opening of the metal additive manufacturing product 2c has a surface (curved surface of a predetermined curvature) that is inclined with respect to the boundary surface with the support member 3c. This makes it possible to reduce the contact of the blade with the vicinity of the opening when removing the support member with a cutting blade, and to further suppress the occurrence of burrs. The radius of curvature of the curved surface of the opening can be, for example, 0.25 mm to 0.50 mm, depending on the range of the area near the outer edge of the opening.

[0027] Next, an outline of the additive manufacturing method of the present invention for a metal additive manufacturing product will be described with reference to Fig. 4. This additive manufacturing method is a method for manufacturing a metal additive manufacturing product having an opening on its surface. This method includes a manufacturing process S1 in which a support member and a metal additive manufacturing product on the support member are manufactured using metal powder as a raw material, and a removal process S2 in which the support member is removed by machining or the like.

[0028] [Building process S1] A known metal powder can be selected depending on the size, shape, and application of the metal additive manufacturing product to be manufactured. Metal powders that can be used as materials are described below. The material of the metal powder is not particularly limited, and examples thereof include alloys containing aluminum, iron, nickel, copper, and cobalt. In addition, alloys containing high-melting point metals such as titanium, vanadium, chromium, zirconium, niobium, molybdenum, tantalum, tungsten, rhenium, and iridium may also be used. The same type of metal powder may be used to manufacture the support member and the metal additive manufacturing product, or different types of metal powder may be used. The average particle size (median diameter) of the metal powder is, for example, in the range of 1 μm to 200 μm.

[0029] Also, a publicly known additive manufacturing device can be selected according to the size, shape, and application of the metal additive manufacturing product to be manufactured. The additive manufacturing device includes a support member and a base plate that serves as a mount for the metal additive manufacturing product when manufacturing the metal additive manufacturing product. On the base plate, a support member is first manufactured, and then the metal additive manufacturing product, which is the target product, is manufactured on the support member. In the manufacturing process S1, a deposition process S1-1 in which metal powder is deposited and a solidified part formation process S1-2 in which a solidified part is formed by irradiating the metal powder at a predetermined location with a laser beam are repeated. In the solidified part formation process S1-2, the metal powder is heated by irradiating the laser beam and sintered or melted. The sintered or melted metal powder becomes a solidified part by cooling. The solidified parts are formed one layer at a time and stacked, and finally a three-dimensional molded product is obtained. The thickness of one layer when the metal powder is deposited is, for example, in the range of 10 μm to 200 μm. The above-mentioned manufacturing process S1 is a manufacturing process when a metal additive manufacturing product is manufactured by the powder bed method, but the additive manufacturing method of the metal additive manufacturing product of the present invention is not limited to this, and a metal deposition method, etc. can also be used. In the case of the metal deposition method, metal powder is deposited by ejecting it from a nozzle only to a predetermined location, and the ejection location is heated by irradiating it with a laser beam to sinter or melt it.

[0030] The shaping of the support member will be described. The support member is formed by stacking solidified metal portions one layer at a time on the base plate. By not irradiating the opening at the interface with the metal additive manufacturing product and the portion in contact with the vicinity of the outer edge of the opening with laser light, no solidified metal portion is formed and the support member is not shaped. As a result, when the support member is completed, the portion becomes a void portion recessed from the interface toward the support member. Meanwhile, the support member is shaped by irradiating the portion other than the void portion located between the metal additive manufacturing product and the base plate with laser light, and supports the metal additive manufacturing product.

[0031] The molding of the metal additive manufacturing product will be explained. After the top layer of the support member is molded, the process moves to molding the metal additive manufacturing product. Here, the layer closer to the base plate is called the lower layer, and the layer farther from the base plate is called the upper layer. In the molding of the first layer of the metal additive manufacturing product, metal powder is deposited and irradiated with laser light to form a solidified part directly above the part where the support member is molded. On the other hand, no solidified part is formed in the part that will become the opening of the metal additive manufacturing product. In addition, a solidified part is formed near the outer edge of the opening. When the deposited metal powder is irradiated with laser light, if the layer below the layered surface is bulk (solidified metal layer), the laser light is irradiated only to the layered surface, and the metal powder in the specified place can be solidified. In this case, the generated heat is rapidly diffused, so the metal powder does not solidify except in the area irradiated with the laser light. On the other hand, in the overhang part, the layer below the layered surface is unsolidified metal powder, so the laser light penetrates into the layer below the layered surface. In other words, the solidification range becomes wider, and the dimensional accuracy deteriorates. In addition, when the lower layer is in a powder state, the thermal conductivity of the metal powder is generally about 1 / 20 to 1 / 100 of the thermal conductivity of the bulk, so heat tends to build up. This can cause the metal powder to sinter not only in the area irradiated with the laser light, but also in the surrounding area, resulting in poor dimensional accuracy. When the width of the overhang, i.e., the distance between the outer edge of the opening and the vicinity of the outer edge, is 1.0 mm or less, it is considered that the laser-irradiated portion of the lamination surface of the overhang is more likely to adhere to the bulk portion near the lower layer than to the lamination surface. As a result, heat is transferred and diffused to the bulk, so that the metal powder in areas other than the area irradiated with the laser light is less likely to sinter, and better dimensional accuracy can be maintained.

[0032] The molding conditions (including the selection of the metal material) for the metal additive manufacturing product and the support member may be the same or different. The laser light intensity may be lower for a shorter time for the support member than for the metal additive manufacturing product, for example. This will result in a lower degree of solidification of the metal of the support member than for the metal additive manufacturing product, shortening the time required to remove the support member and reducing the burden on the tools, which is expected to extend the tool life.

[0033] From the viewpoint of forming the voids into a predetermined shape, it is preferable that the thickness of one layer when depositing the metal powder is smaller than the height of the voids in the stacking direction. This allows the voids to be formed into any shape (for example, the dome shape in FIG. 1). In addition, when multiple openings are arranged on the boundary surface between the metal additive manufacturing product and the support member and are arranged closer than a predetermined distance or in contact with each other, resulting in an excessively overhanging shape, a support member may be provided in the overlapping portion of the voids.

[0034] [Removal process S2] When the formation of the support member and the metal additive manufacturing product is completed, the process proceeds from the forming process S1 to the support member removal process S2. In the removal process S2, the supported product is removed from the base plate. The support member of the removed supported product is removed by machining such as cutting and polishing using a metal processing tool or the like. The machining such as cutting and polishing can be performed, for example, by a cutting blade. If high smoothness is required, electrolytic polishing or surface treatment using chemicals may be performed as a finishing process after the machining.

[0035] When the support member is removed with a cutting blade, the lower surface of the support member removed from the base plate is brought into contact with the cutting blade rotating at high speed. In this case, if the outer edge of the gap in the support member and the outer edge of the opening of the metal additive manufacturing product are in the same position when viewed from the stacking direction, the cutting blade comes into direct contact with the outer edge of the opening, which is likely to cause burrs. In contrast, in the additive manufacturing method of the present invention, a gap is provided in the portion in contact with the opening and the vicinity of the outer edge of the opening, minimizing the contact of the cutting blade with the vicinity of the opening, making it difficult for the cut support member to enter the inside of the opening, and suppressing the occurrence of burrs.

[0036] The design method of the support member of the present invention will be described below. This support member is used in an additive manufacturing method for a metal additive manufacturing product having an opening on its surface. This design method is a method for designing an optimal support member for simplifying the support member removal process according to the shape, position, size, number, etc. of the opening on the surface of the metal additive manufacturing product. More specifically, this is a method for designing a support member that is easy to remove from a supported product and that can obtain a metal additive manufacturing product with the target dimensions after removal. This design method is also a method for designing a support member that is less likely to shorten the life of the tool used in the support member removal process.

[0037] This design method is characterized in that the shape of the support member is set so that the opening at the interface with the metal additive manufacturing product and the portion in contact with the vicinity of the outer edge of the opening are voids recessed from the interface. The design of the support member is performed following the design of the metal additive manufacturing product, which is the final target. The location of the support member on the surface of the metal additive manufacturing product is determined based on information such as the overall shape of the metal additive manufacturing product and the shape, position, size, and number of openings on the surface. If the metal additive manufacturing product has openings on multiple surfaces with different angles, multiple support members may be provided. The support member may be provided, for example, not only on the lower surface located between the metal additive manufacturing product and the base plate in the modeling process, but also on the side surface.

[0038] An example of a supported laminate designed by this design method will be described with reference to Figure 5. Figure 5 shows the cross-sectional view shown in Figure 3(a) and its enlarged view. 5, the shape of the support member 3a is set so that the outer edge 32a of the void 31a is positioned a certain distance X outward from the outer edge 23a of the opening 22a of the metal additive manufacturing product 2a. As a result, as described above, when carrying out the additive manufacturing method, it is possible to suppress the generation of burrs at the opening and to simplify the support member removal process.

[0039] The thickness Y1 of the support member 3a is desirably a certain thickness or more from the viewpoint of stably performing polishing and cutting when removing the support member and obtaining a metal additive manufacturing product having a smooth surface and the target dimensions. Also, from the viewpoint of extending the life of the tool used to remove the support member 3a, the thickness Y1 of the support member 3a is preferably thinner than a predetermined thickness. The thickness Y1 of the support member 3a is set by taking into account these factors.

[0040] The height Y2 of the gap 31a can be freely selected within a range in which no burrs are generated inside the opening 22a. Moreover, it is preferable that the height Y2 of the gap 31a is smaller than the thickness Y1 of the support member 3a. It is more preferable that the height Y2 of the gap 31a satisfies the relationship height Y2≦distance X≦1.0 mm. This can reduce the area (gap) where different loads are intermittently applied to the tool during the support member removal process, thereby extending the life of the tool.

[0041] In addition, various structures of the gaps in the support members described above can also be appropriately incorporated into this design method.

[0042] This design method can also be made into a system that automatically designs the shape and installation location of support members based on the design information of the metal additive manufacturing product. This allows the design information of the support members to be obtained while designing the metal additive manufacturing product, making it possible to predict problems that may occur during manufacturing from the design stage of the metal additive manufacturing product. As a result, in addition to simplifying the support member removal process, it is possible to save time and effort spent on trial and error by repeating the modeling and removal processes, facilitating the development of metal additive manufacturing products.

[0043] As an example of the modeling process of the present invention, an outline of the modeling process for manufacturing a metal additive manufacturing product by the powder bed method will be described. This modeling method is widely used because of its excellent reproducibility and dimensional accuracy. There is no particular limitation on the additive manufacturing device for this method, but for example, the following configurations can be used.

[0044] Fig. 6 is a schematic diagram showing an example of a molding process using the powder bed method, in which (a) shows a deposition process in which metal powder is deposited, and (b) shows a solidified portion formation process in which a laser beam is irradiated onto the metal powder to form a solidified portion. The additive manufacturing apparatus 4 is equipped with a lifting means 42 that can be raised and lowered and has a base plate 41 at its upper end, and around this base plate 41, there are provided a supplying means 43 that supplies metal powder 50 onto the base plate 41, a depositing means 44 that deposits the supplied metal powder 50 in a thin layer on the base plate 41, and a heating means 45 that heats the metal powder 50 for sintering or melting it. These devices are housed in a chamber, and the atmosphere within the chamber is a vacuum atmosphere or an inert gas atmosphere such as argon gas or nitrogen gas depending on the type of heating means, and the internal pressure and temperature may be controllable.

[0045] In the deposition step shown in Fig. 6(a), metal powder 50 is deposited in a thin layer on a base plate 41. In the solidified portion formation step shown in Fig. 6(b), the metal powder 50 in a predetermined position is irradiated with laser light from heating means 45 to sinter or melt and form a solidified portion. The above two steps are repeated alternately to form a metal additive manufacturing product consisting of a collection of solidified portions.

[0046] The details of these steps are described below. First, the upper surface of the base plate 41 of the additive manufacturing apparatus 4 is spaced a predetermined distance from the bottom of the deposition means 44. At this time, the height of the deposition means 44 is kept constant, and the predetermined distance is achieved by adjusting the height of the base plate 41. In the deposition process, the metal powder 50 supplied from the supply means is deposited in a thin layer on the base plate 41 by the deposition means 44. Specifically, the metal powder 50 is deposited by the plate-shaped deposition means 44 moving horizontally while keeping a constant distance from the upper surface of the base plate 41, and spreading the metal powder 50 while scraping it down.

[0047] The thickness of the layer of the deposited metal powder 50 can be adjusted by the distance between the upper surface of the base plate 41 and the bottom of the depositing means 44. The thickness of the layer of the metal powder 50 is preferably set to a value larger than the particle size of the metal powder 50. This makes it easier to ensure the thickness of the layer of the metal powder is uniform, making it easier to ensure the molding precision and uniformity of the solidification structure of the metal additive manufacturing product.

[0048] In the solidified portion forming process, a laser beam emitted from the heating means 45 is irradiated while being scanned at a predetermined position of the metal powder 50 spread on the base plate 41, thereby partially sintering or melting the metal powder 50. The temperature of the portion irradiated with the laser beam drops, and when the temperature falls below the melting point, the portion solidifies.

[0049] By performing the deposition step and the subsequent solidified portion forming step once each, one layer can be molded. After one layer has been molded, the base plate 41 is lowered by the lifting means 42 by the thickness of the layer to be molded next. Following the lowering of the base plate 41, the above-mentioned deposition of the metal powder 50 and the formation of the solidified portion are performed again, thereby molding the next layer on the previously molded layer. In this way, by repeating the deposition step, the solidified portion forming step, and the lowering of the base plate, the metal solidified portions are piled up, and a support member and a metal additive manufacturing product are molded.

[0050] When a supported product is manufactured by the above process, the portion not irradiated with the laser light remains as metal powder together with the product in the manufacturing device until the manufacturing of the supported product is completed. Therefore, when the support member is manufactured, the manufacturing proceeds with the void portion filled with metal powder. After the support member is manufactured, when the solidified portion of the first layer of the metal additive manufacturing product is formed, the deposited metal powder is irradiated with laser light at a location other than the opening to form the solidified portion. At this time, the laser is also irradiated near the outer edge of the opening of the metal additive manufacturing product, but the metal powder of the support member is located directly below the portion irradiated with the laser light. Although the shape of the solidified portion itself is an overhang shape, the portion irradiated with the laser light on the layered surface of the overhang portion adheres to the bulk portion near the lower layer of the layered surface, so that the heat is transferred to and diffused into the bulk, thereby forming an overhang shape.

[0051] After the modeling process is completed, the supported model is removed from the additive manufacturing device, and the unsolidified metal powder is removed with high-pressure air. The support member side of the model is then pressed against a cutting blade rotating at high speed to remove the support member. In the support member removal process, contact of the cutting blade with the opening is minimized. By applying the additive manufacturing method of the present invention to powder bed additive manufacturing, a metal additive manufacturing product with excellent dimensional accuracy and no burrs inside the opening can be obtained. EXAMPLES

[0052] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the following examples.

[0053] Examples 1 to 5, Comparative Examples 1 and 2 In order to study the effect of the condition around the opening on the generation of burrs in the support member removal process, supported molded products having seven types of through holes with different shapes of voids and openings were molded. The supported molded products were flat, and n=5 through holes and the like were molded in one supported molded product for each condition. The shapes of the voids and openings were determined by the combination of the distance X between the outer edge of the opening and the outer edge of the void, the height Y2 of the void, and the radius of curvature R of the opening shown in FIG. 5. The conditions of the examples and comparative examples are shown in Table 1. In Table 1, C1 to C5 are the conditions of Examples 1 to 5, and C6 and C7 are the conditions of Comparative Examples 1 and 2.

[0054] [Table 1]

[0055] In Examples 1 to 5, X is 0.25 mm or 0.50 mm, and when viewed from the stacking direction (when viewed in the through-hole direction), the outer edge of the gap is located outside the outer edge of the opening. In contrast, in Comparative Examples 1 and 2, X is 0 mm, and when viewed from the stacking direction, the outer edge of the gap and the outer edge of the opening are in the same position.

[0056] FIG. 7 shows the design drawing of the supported molded product used in this experiment. FIG. 7(a) is a side view of the supported molded product, and FIG. 7(b) is a plan view of the metal additive manufacturing product after the support members have been removed, viewed from the opening side. As shown in FIG. 7(a), the thickness of the metal additive manufacturing product 2 in the through-hole penetration direction is 20.0 mm, and the thickness of the support members in the through-hole penetration direction is 5.0 mm. Also, as shown in FIG. 7(b), the inner diameters of all the through holes are 1.0 mm.

[0057] The support members were removed from the supported object formed by the powder bed method so as to have the shape shown in Figure 7(a) by the following method. 1. The machining surface (the boundary between the metal additive manufacturing product and the support material) is machined using a milling machine, leaving 0.50 mm of support material. 2. Leave a 0.10 mm support material on the machining surface and cut using a milling machine. 3. Leave a 0.05 mm support material on the machining surface and cut using a milling machine. 4. Process up to the machining surface.

[0058] Fig. 8 shows an image of the entire machined surface after the support members have been removed. Fig. 9 shows an enlarged image of the openings after the support members have been removed. In Comparative Examples 1 and 2 (conditions C6 and C7), burrs were generated over the entire openings, blocking the through holes. In contrast, in Examples 1 to 5 (conditions C1 to C5), the openings were fully open, and burr generation was significantly suppressed. Note that in Fig. 8, the reason there are no burrs in the second and third holes from the top in Condition C6 is because they were removed for confirmation during the experiment.

[0059] As described above, the additive manufacturing method of the present invention can suppress the occurrence of burrs at the openings when manufacturing a metal additive manufacturing product having openings on its surface, simplifying the support member removal process, and extending tool life. [Explanation of symbols]

[0060] 1: Model with support 2, 2a, 2b, 2c: Metal additive manufacturing products 21:Through hole 22, 22a: Opening 23, 23a, 23b, 23c: outer edge 3, 3a, 3b, 3c: Support members 31, 31a, 31b, 31c: void area 32, 32a, 32b, 32c: outer edge 4: Additive manufacturing equipment 41: Base plate 42: Lifting means 43: Supply means 44: Deposition means 45:Heating means 50: Metal powder

Claims

1. A method for additive manufacturing of a metal additive manufacturing product having an opening on a surface thereof, comprising the steps of: The additive manufacturing method includes a manufacturing step of manufacturing a support member and the metal additive manufacturing product on the support member, and a removal step of removing the support member by machining, the manufacturing process is a process of manufacturing the support member and the metal additive manufacturing product by repeating deposition of metal powder and sintering or melting the metal powder by irradiating it with laser light, The support member has an opening and a portion in contact with the metal additive manufacturing product at a boundary surface thereof, the portion being a void recessed from the boundary surface; An additive manufacturing method, characterized in that, in the manufacturing step, a cross section of the void portion parallel to the stacking direction is formed into a rectangular shape.

2. The layered manufacturing method according to claim 1 , wherein the vicinity of the outer edge is within a range of up to 1.0 mm from the outer edge of the opening.

3. The additive manufacturing method according to claim 1 or 2, wherein in the manufacturing step, a surface that is inclined with respect to a boundary surface with the support member is formed on an outer edge of the opening of the metal additive manufacturing product.

4. A method for additive manufacturing of a metal additive manufactured product having an opening on a surface, comprising the steps of: The additive manufacturing method includes a manufacturing step of manufacturing a support member and the metal additive manufacturing product on the support member, and a removal step of removing the support member by machining, the manufacturing process is a process of manufacturing the support member and the metal additive manufacturing product by repeating deposition of metal powder and sintering or melting the metal powder by irradiating it with laser light, The support member has an opening and a portion in contact with the metal additive manufacturing product at a boundary surface thereof, the portion being a void recessed from the boundary surface; An additive manufacturing method, characterized in that, in the manufacturing process, a surface that is inclined with respect to the boundary surface with the support member is manufactured on the outer edge of the opening of the metal additive manufacturing product.

5. A method for designing a support member for supporting a metal additive manufacturing product, which is used in a method for additive manufacturing of a metal additive manufacturing product having an opening on a surface, comprising: The additive manufacturing method is a method of repeatedly depositing a metal powder and sintering or melting the metal powder by irradiating it with a laser beam to form the support member and the metal additive manufacturing product on the support member, and then removing the support member by machining; The shape of the support member is set so that a portion of the support member that is in contact with the opening and the vicinity of the outer edge of the opening at the boundary surface with the metal additive manufacturing product is a void portion recessed from the boundary surface; A method for designing a support member, comprising forming the void portion so that a cross section of the void portion parallel to the stacking direction is rectangular.

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